Functionalized Carbon Nanotubes for the Electrochemical Quantification of Renin as a Marker of Tissue-Perfusion

Renin is an enzyme with the function to produce angiotensin I in plasma triggering a cascade of reactions that regulate blood pressure homeostasis. It is a useful marker of tissue perfusion plasma renin activity (PRA), but it was not well exploited in terms of electroactivity in human blood while evaluating the renin-angiotensin-aldosterone system. To quantify the renin levels in human plasma samples, a novel screen-printed carbon electrode (SPCE) sensor modified with doped multi-walled carbon nanotubes (MWCNTs) and polyethylene glycol (PEG) is proposed and experimentally demonstrated. PEG is a biopolymer commonly used to coat the surface of nanostructures to reduce nonspecific interactions and minimize aggregation promoting colloidal stability. The functionalized MWCNTs were first evaluated with Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) images. The structural analysis proved that there were no further effects on the size and shape of the carbon nanostructures. The doping was confirmed with the three-electrode cyclic voltammetry (CV) technique where the peak currents were amplified by almost 6.5× after the functionalization step. Afterward, the Human Renin Antibody Pair is immobilized on the nanocomposite film for 1 hour before the performance of the electrochemical measurements with the samples containing the enzyme. Differential pulse voltammetry (DPV) measurements were performed to quantify the Renin (0 ~ 2,000 pg/mL) in human plasma samples (<20 μl) that are injected into the device. The variation of the current peaks presented high linearity (linear regression coefficient (R²) of 0.9890) with the levels of renin enzyme. The validation was obtained while comparing the results of the SPCE device with the gold standard method, Enzyme-Linked Immunosorbent Assay (ELISA), using the Bland–Altman plot with a good agreement between the two methods within a 95% confidence interval. Further studies involve the combination with the other inflammation-related markers already evaluated with our multiplexed electrochemical sensing device.